Released in the US as Godzilla vs. The Thing (I don't know why), Mothra is refered to as "the thing" in most of the scenes, but listen closely and you hear "Mothra" every now and again.

It seems that atomic testing has reduced Mothra's home on Infant Island to ruins and greedy Japanese business men have taken her egg and are charging admission to view it -- Mothra is POed and wants it back.

Here come the twin fairies to plead for the return of Mothra's egg but the only thing they accomplish is to get the geedy executives wanting to put the fairies on display! Bad mistake, because Godzilla wakes up and he ain't a morning person! Only Mothra can stop Godzilla but will she after the way man has treated her?